Proposal (1050) to South American Classification Committee

Modify classification of the Ardeidae: (A) change the linear sequence and (B) add subfamilies

Note from Remsen: This is another proposal relayed from NACC, which passed both parts. Note that much of the background material is not directly relevant to SACC because our baseline classification did not subdivide the Ardeidae into subfamilies or tribes.

Background:

Our current linear sequence of the family Ardeidae is unchanged since the seventh edition of the Checklist (AOU 1998), where the notes for the family are as follows:

“Recent studies of genetic and vocal characters (Sheldon 1987[a], Sheldon et al. 1995, McCracken and Sheldon 1997) support the traditional arrangement used here in most ways; the relationships of Butorides might be with the Nycticoracini rather than the Ardeini.”

Curiously, as might be deduced from this note, the family was divided into tribes rather than subfamilies. Four tribes were recognized (genera in our area are in parentheses):

1. Botaurini: Bitterns (Botaurus and Ixobrychus)

2. Tigrosomatini: Tiger-Herons (Tigrisoma)

3. Ardeini: Typical Herons (Ardea, Egretta, Bubulcus, Butorides, Agamia, and Pilherodius), and

4. Nycticoracini: Night-Herons (Nycticorax, Nyctanassa, and Cochlearius).

Numerous molecular studies of herons have been published more recently than AOU (1998), including Sheldon et al. (2000), Chang et al. (2003), and Huang et al. (2016), but many questions remain concerning relationships among species and genera in this family and higher-level divisions (subfamilies or tribes) within the family. Kushlan and Hancock (2005), for example, divided the family into five subfamilies:

1. Tigrisominae (tiger herons)

2. Botaurinae (bitterns)

3. Ardeinae (typical herons, including night herons)

4. Agamiinae (Agami Heron Agamia agami), and 

5. Cochleariinae (Boat-billed Heron Cochlearius cochlearius). 

New Information:

Hruska et al. (2023) recently published a phylogenetic paper on herons based on sequences of UCEs and mitochondrial DNA. They sampled 55 species of heron, although success with both UCEs and mtDNA was variable: 46 species were included in their UCE tree (Fig. 1), and 47 species in their mtDNA trees (Figs. 2, 3).

Fig. 1. Phylogenetic tree based on sequences of UCEs (Hruska et al. 2023). All nodes received 100% bootstrap support except as noted.

This phylogeny recovered the subfamily structure of Kushlan and Hancock (2005), although the species composition of subfamilies differed somewhat and the subfamily name Tigriornithinae (Bock 1956) was used instead of Tigrisominae for the tiger-herons. Support for relationships in the UCE tree was universally high: all nodes received 100% bootstrap support with the exception of the node uniting all species of the Ardeinae except for Gorsachius melanolophus, which was 88%. The mitochondrial phylogenies (Maximum Likelihood and Bayesian) recovered the same subfamily structure (except that Agamia agami was not sampled, and so Agamiidae was not identified) and the same relationships among subfamilies, although many bootstrap values were not as high, and the trees lacked resolution in some areas:

Fig. 2. Phylogenetic tree based on Maximum Likelihood analysis of sequences of mtDNA (Hruska et al. 2023). All nodes received 100% bootstrap support except as noted.

Fig. 3. Phylogenetic tree based on Bayesian analysis of sequences of mtDNA (Hruska et al. 2023). All nodes received 100% bootstrap support except as noted.

Recommendation:

I recommend that we adopt the linear classification posted at the end of this proposal, as well as the following sub-family classification (to replace the tribes used in AOU 1998):

1. Tigriornithinae (tiger herons)

2. Cochleariinae (Boat-billed Heron Cochlearius cochlearius)

3. Agamiinae (Agami Heron Agamia agami)

4. Botaurinae (bitterns)

5. Ardeinae (typical herons, including night herons)

Note that Tigriornithinae Bock, 1956, the subfamily name used by Hruska et al. (2023), apparently has priority over Tigrisomatinae and Tigrisominae. The latter names, as far as I’m aware, were first used by Payne & Risley (1976) and Kushlan & Hancock (2005), respectively. (Thanks to David Donsker for tracking down these references.)

Terry Chesser, May 2025

Note from Remsen on SACC voting structure:

A. A YES vote means you are in favor of changing the SACC linear sequence. A NO vote means you favor retaining the status quo or some other sequence (please elaborate).

B. A YES vote means you are in favor of adding the subfamily structure to the SACC list as per the NACC proposal.

Note also that the hyphens in “Night-Heron” are removed automatically (as per our recently agreed-upon policy) because these recent data indicate that they are not a monophyletic group, e.g. distantly related Old World Gorsachius species also called “Night Heron”.

Note also that the sequence and classification does not yet consider the current SACC proposal to place Bubulcus in Ardea or a forthcoming proposal on the inclusion of Ixobrychus in Botaurus.

Our current classification is as follows.

ARDEIDAE (HERONS) 1

Tigrisoma lineatum Rufescent Tiger-Heron

Tigrisoma fasciatum Fasciated Tiger-Heron

Tigrisoma mexicanum Bare-throated Tiger-Heron

Agamia agami Agami Heron

Cochlearius cochlearius Boat-billed Heron

Zebrilus undulatus Zigzag Heron

Botaurus pinnatus Pinnated Bittern

Ixobrychus exilis Least Bittern

Ixobrychus involucris Stripe-backed Bittern

Nycticorax nycticorax Black-crowned Night-Heron

Nyctanassa violacea Yellow-crowned Night-Heron

Butorides striata Striated Heron

Butorides virescens Green Heron

Ardeola ralloides Squacco Heron (V)

Bubulcus ibis Cattle Egret

Ardea cinerea Gray Heron (V)

Ardea herodias Great Blue Heron

Ardea cocoi Cocoi Heron

Ardea purpurea Purple Heron (V)

Ardea alba Great Egret

Syrigma sibilatrix Whistling Heron

Pilherodius pileatus Capped Heron

Egretta tricolor Tricolored Heron

Egretta rufescens Reddish Egret

Egretta gularis Western Reef-Heron (V)

Egretta garzetta Little Egret (V)

Egretta thula Snowy Egret

Egretta caerulea Little Blue Heron

If both A and B pass, then our new classification would be as follows (following SACC’s standard linear-sequencing conventions and using the UCE phylogeny above, Fig. 1):

ARDEIDAE (HERONS)

Tigriornithinae

Tigrisoma lineatum Rufescent Tiger-Heron

Tigrisoma mexicanum Bare-throated Tiger-Heron

Tigrisoma fasciatum Fasciated Tiger-Heron

Cochleariinae

Cochlearius cochlearius Boat-billed Heron

Agamiinae

Agamia agami Agami Heron

Botaurinae

Zebrilus undulatus Zigzag Heron

Ixobrychus involucris Stripe-backed Bittern

Ixobrychus exilis Least Bittern

Botaurus pinnatus Pinnated Bittern

Ardeinae

Pilherodius pileatus Capped Heron

Syrigma sibilatrix Whistling Heron

Egretta caerulea Little Blue Heron

Egretta tricolor Tricolored Heron

Egretta rufescens Reddish Egret

Egretta thula Snowy Egret

Egretta garzetta Little Egret (V)

Egretta gularis Western Reef-Heron (V)

Nyctanassa violacea Yellow-crowned Night Heron

Nycticorax nycticorax Black-crowned Night Heron

Butorides striata Striated Heron

Butorides virescens Green Heron

Ardeola ralloides Squacco Heron (V)

Bubulcus ibis Cattle Egret

Ardea alba Great Egret

Ardea cinerea Gray Heron (V)

Ardea herodias Great Blue Heron

Ardea cocoi Cocoi Heron

Ardea purpurea Purple Heron (V)

Voting Chart: https://www.museum.lsu.edu/~Remsen/SACCPropChart1044+.htm

Comments from Bonaccorso: “YES. The subfamilies and the sequences agree with the available evidence, both nuclear and mitochondrial.”

Comments from Remsen:

“A. YES. I re-checked the NACC sequence and found no problems.

“B. YES. We don’t have a specific policy on when to use subfamilies or a definition for “subfamily”. The category is widely used to demarcate deep divisions within a group, and thus I find it useful when talking about that group. So, if other people add subfamilies to their classifications, I have no objection as long as that is the intent.”